1. Field of the Invention
The invention relates to fabrics having improved optical properties and a process for the preparation thereof. More particularly, the invention relates to fabrics having an improved color developing property enabling them to exhibit a high depth of color when dyed or otherwise colored.
2. Description of the Prior Art
Methods of rendering a depth of color to fibers have hitherto been proposed, for example, in U.S. Pat. No. 4,254,182 and Japanese Laid-open Patent Application No. 52-99400 in which the depth of color is developed by forming fine recesses and projections on the surface of the fibers, whereby light incident in the recesses is reflected within the recesses so that the reflection of the incident light from the fiber surface is reduced.
Japanese Laid-open Patent Application No. 52-99400 claims the following inventions:
(1) a synthetic fiber having a finely rugged surface, characterized in that recesses and projections of 0.1 to 0.5 .mu.m are formed on the overall surface of the fiber at a density of 10 to 200 per .mu.m.sup.2 ;
(2) a process for preparing a synthetic fiber having a finely rugged surface, characterized in that recesses and projections of 0.1 to 0.5 .mu.m are formed on the surface of the fiber by subjecting an organic synthetic fiber to plasma irradiation by means of glow discharge; and
(3) a process for preparing a synthetic fiber having a finely rugged surface as in (2) above in which the glow discharged plasma is irradiated to the fiber under discharge conditions in which the current density is 0.1 to 5.0 mA/cm.sup.2 and the plasma dose is 80 to 500 mA.sec/cm.sup.2.
The U.S. Patent and the Japanese laid-open patent application do not disclose that the fiber is coated with a coating material of a specific refractive index to a specific thickness. In the prior art fiber, the finer the recesses and projections on the fiber surface, the higher the depth of color of the fiber. However, if the recesses and projections are very fine, the fiber surface readily becomes smooth due to abrasion of the recesses and projections so that the depth of color of the worn portion is reduced, that is, the color lightens and is nonuniform. Therefore, the prior art fiber can not have a high depth of color as in natural fibers since the recesses and projections can not be formed so finely that the above-mentioned abrasion problem does not seriously occur.